While habitat destruction ranks as the number one reason for loss of species and biodiversity, the invasion of exotic species (aka invasives) ranks number two. When aggressive invasives crowd out a native species it can often have a ripple effect on other native species.
One example of this that has happened while I have lived in Texas is the decline of the Texas horned lizard (aka horned toad). When I was in high school I was lucky enough to see some horned lizards in their native habitat. We also had a large harvester ant nest near the back of the pasture. At the time I didn't know about the link between that ant mound and the horned lizards. The ants didn't cause any trouble though so we left them alone.
Unfortunately, the invasive fire ants did cause trouble for the native harvester ants. They crowded them out and took over their territory. This spelled trouble for the horned lizard. Harvester ants are their main source of food. Isn't any ant as good to eat as another, you may ask? Unfortunately not, or at least not as easy to eat. The way fire ants swarm make them difficult for the horned lizard to make a meal of them without getting harmed. The horned lizard is now a protected species, due in large part, to the ripple effect of invasive fire ants crowding out the horned lizard's main food source, the harvester ant.
While it is unlikely that I will get a chance to spy a horned lizard in my area of Texas anymore, I did get excited that I might have actually seen one a few years ago. I caught a glimpse of a brown, spiky lizard. However as I was trying to remember exactly what a horned lizard looked like from many years before, the lizard turned around and it had a very long tail. Then I knew it wasn't a horned lizard. I did a bit of research and found out that the mystery lizard was a Texas spiny lizard. They are slimmer, not as spiky and have a longer tail than the horned lizard. While I miss seeing those iconic "horny toads", my property seems to have become a haven for the spiny lizard. That is a good thing for me since their diet consists of a wide range of insects.
But I digress, back to the plight of the TX horned lizard and other native plants and animals that suffer at the spread of invasives. You can help by educating yourself about invasives so you don't help them spread and by participating in citizen scientist projects like the Lady Bird Johnson Wildflower Center's Sentinel Pest Network and Invaders of Texas Program that the center partners with.